Systems and methods for analysis of ECG signals are known. For example, U.S. Pat. No. RE 43569 to Olson discloses methods for identifying ischemia conditions/cardiac infarction by analysis of ECG vector signals. Systems and methods that analyze ECG (vector) signals to simply and accurately localize cardiac volumes or segments in which a coronary vessel likely responsible for an ischemic condition are heretobefore unknown.
When the blockage in a single coronary artery occurs it has been found that the location of that coronary artery tree can be associated with the loss of circulation in a selected number of segments of the heart. The inventive systems and methods described herein operate to automatically measure ischemic levels in cardiac segments to determine which coronary artery or segment thereof is responsible for the ischemia and to provide a visual presentation of the heart that clearly and readily identifies the ischemic and/or infarcted area or areas.
The relationship between vectors and heart segments was originally explored by Olson, C W, Warner R A, Wagner G S, Selvester R H S, A DYNAMIC THREE-DIMENSIONAL DISPLAY OF VENTRICULAR EXCITATION AND THE GENERATION OF THE VECTOR AND ELECTROCARDIOGRAM, J. Electrocardiology 2001, 34 (Suppl), pp. 7-15, 2001 (Olson, et al.); R. S. Selvester, G. S. Wagner. R/E. Ideker, “Myocardial Infarction” Chapter 16 “Comprehensive Electrocardiology,” p. 565 (1989); and is pictured in a Mercator projection of the left ventricle (FIG. 1). That is, FIG. 1 provides Mercator projection diagram of the Left Ventricle separated into 12 segments. The vertical or ordinate axis is segmented in millimeter (mm) to depict the vertical dimension. The horizontal or abscissa axis extends 360 degrees (azimuth) from −180 to 180 degrees (with reversal at −135 degrees), to depict the surface of the epicardium in a 2D projection.
This Mercator projection diagram highlights that there are 3 main coronary arteries, Left Anterior Descending (LAD), Left Circumflex (LCX) and Right Coronary Artery (RCA). Each of these coronary arteries profuse a chain of segments of the heart, i.e., segment numbers 1-12 (see FIG. 1).
Identifying the ischemic segments, i.e., the segment or segments affected by a blockage of one of these coronary arteries leads to identification of the responsible (blocking) coronary artery as well as the extent and region of the blockage and possible damage to the heart tissue in the segment or segments that is/are nourished by the blocking artery. Such critical information is used to determine the treatment required at an early stage and, therefore, lessen the damage done to the cardiac tissue as a result of the blockage/ischemia.
The quickest and easiest way to recognize an ischemic event is through the use of the Electrocardiograph (ECG). Hence, ECG analysis is one of the first diagnostic tests that are administered in an ambulance, helicopter, etc. (e.g., by a first responder) for a patient with suspected heart attack.
The lead system that is most prevalent in ambulances and hospitals is the 12 lead ECG although the principles applied here could be applicable to other lead arrangements. Many years ago, Ernest Frank, PhD, disclosed a method of measuring the image surface of the homogenous human torso. Dr. Frank started with a model of the human torso and divided it into 12 horizontal slices, as shown in FIG. 2. Dr. Frank took points on the torso in horizontal slices at 2″ spacing, number 1-12. Each slice is a cross section, where each cross section also is split or divided into pie sections from the center that have a 22.5 degree radial dimension. To use the Frank model, electrodes are attached at each point of the torso as determined from these cross sections (i.e., volumetric segments). Measurements of the voltage are made at each point on the torso in response to a unit current dipole located at the electrical center of the heart as determined from the torso geometry. The torso is filled with a conducting fluid to simulate the body tissue characteristics. The techniques are described in detail in the paper, Frank, E. “The image surface of a homogeneous torso”, Am Heart J. 47:757 1954; Milan Horacek “Lead Theory”, Chapter 10 “Comprehensive Electrocardiology” p. 291-314, (1989); MacFarlane, P. “Lead Systems” Chapter 11 “Comprehensive Electrocardiology” p 315-352. MacFarlane also showed that other locations on the heart may be used as a source for the dipole as may be related to the location of the ischemia; MacFarlane, P, Veitch Lawrie; “Comprehensive Electrocardiology” Volume I, Pergamon Press New York (1989).
From the measurement of the voltages at each point on the body, a contour of each of the 12 slices (image surfaces in the horizontal plane) is/was created for the horizontal plane, as shown in FIG. 3. The measurement of the voltage at each of the points on the surface give the contours for each level as numbered. These points at each level are plotted with the letters showing the horizontal angular locations. The lead vectors for the precordial leads are shown on the diagram and give the magnitude and direction of the response of each lead from the torso surface to the Wilson terminal near the center.
The resultant contour is called the image surface and is extremely useful for finding the direction vectors between points on the body or from any point to the Wilson central terminal, which is indicated. Please note that Wilson terminal was explained in: Peter Macfarlane, “Lead Systems” Chapter 11 “Comprehensive Electrocardiology” (p. 315).